D. Increasing data implicate cytokines in the development of behavioral alterations in patients with a wide range of medical illnesses including cancer;patients with medical illnesses exhibit rates of depression 5-10 times higher than the general population. Depression in the medically ill is associated with reduced treatment adherence, impaired quality of life, and in several studies, increased morbidity and mortality. Model systems to study the neurobiology and treatment of cytokine-induced depression are needed to develop new strategies to help diagnose and manage depression in the medically ill. One such model system involves patients receiving the cytokine interleukin (IL)-2. This T cell cytokine is used to treat patients with cancer and causes profound behavioral alterations including depressed mood, anhedonia, anorexia, fatigue, cognitive dysfunction (especially memory impairment), altered sleep and psychosis, symptoms that overlap with many of those of major depression. In addition, IL-2 potently activates the hypothalamic-pituitary adrenal (HPA) axis and alter neuretransmitter metabolism, while activating the release of other cytokines (e.g.lL-6) that have been implicated in mood disorders. We plan to characterize neuropsychiatric, neuroendocrine and immune changes in patients undergoing IL-2 treatment for malignant melanoma and evaluate whether an antidepressant can prevent these changes. 70 patients with Stage IV malignant melanoma (ages of 18 to 75 years old) will be studied before and during intravenous (IV) IL-2 treatment [720,000 units/kg Q8 hours X 5 days (1 cycle) every 3 weeks X 4 cycles]. Two weeks prior to IV IL-2 therapy, patients will enter a randomized, double-blind treatment trial comparing 14 weeks of treatment with the antidepressant paroxetine, versus placebo. We will determine whether paroxetine will: a) diminish IL-2-associated neuropsychiatric symptoms, b) reduce IL-2-associated increases in ACTH and cortisol and increase glucocorticoid sensitivity, c) prevent IL-2-induced decreases in serotonin metabolism as manifested by decreased plasma tryptophan and 5HT and increased plasma kyneurinine, and d) improve the number of IL-2 doses tolerated. We will also correlate specific neuropsychiatric symptoms (including memory impairment and psychosis) with HPA axis and immune function both prior to, and during, IL-2 therapy, and determine the impact of paroxetine on these relationships. These studies will provide insights into differential mechanisms of symptom development and treatment response during cytokine therapies.